It will be apparent from the following disclosure that the present invention has particular utility in conjunction with four-way type plug valves. It should be borne in mind, however, that the present invention also has utility from the standpoint of rotary plug valves other than four-way plug valves. For purposes of simplicity, however, the invention is described particularly as it relates to four-way plug valve mechanisms.
Plug valves may be classified in three basic classes, i.e. cylindrical plug valves, tapered or conical plug valves and spherical plug valves, which are commonly referred to as ball valves. With regard specifically to tapered plug valves, these may be classified as simple rotary valves wherein the plug element is simply rotated within the valve body for controlling the flow of movement through the valve mechanism. In order to protect the sealing elements and sealing surfaces of tapered plug valves from excessive wear, plug valves have been developed that are operated by lifting the tapered plug element or shifting it linearly to unseat or separate the sealing element of the plug from the seating surfaces defined within the valve body. After the unseating movement, the plug element is then rotated to the proper position and is then moved linearly in the opposite direction to again seat the sealing element of the plug in sealing engagement with the seating surfaces of the valve body. As the plug element is rotated during operation of the valve mechanism, the sealing element often carried by the plug is not in engagement with any internal seating surfaces and therefore no wear occurs during such movement. The service life of such lift-turn type plug valves is therefore materially enhanced. Providing a lift-turn capability for plug valve mechanisms is especially important when large plug valves are mployed because of the length of seal travel during operational movements.
When four-way type lift plug valve mechanisms are incorporated in meter prover systems, it is necessary for such valve mechanisms to be cycled quite frequently. It is therefore desirable to provide a plug valve mechanism that does not become excessively worn because of rapid, frequent cycling.
Where large plug valves are employed in fluid flow control apparatus, such as flowmeter loops, the valve mechanisms are typically cycled quite rapidly, i.e. moved from one operative position to another in a period of several seconds duration. Where the plug valve mechanisms are of large size, the internal rotatable plug elements will be quite massive and will have considerable weight. Typically, forces of inertia necessary to start and stop the rotational movement of the plug element is absorbed by the structural components of the valve actuator that achieves linear and rotational movement of the plug. Because of the severe inertia forces that are transmitted to the valve actuator system are quite severe, the valve actuator mechanism is typically of extremely durable and expensive manufacture in order to compensate for these forces as much as possible. Ordinarily, inertia forces are not excessively severe as rotational movement of the plug element is initiated. At the end of the rotational stroke, however, the valve actuator is suddenly stopped and a severe inertial force will be transmitted from the plug member through the valve actuator mechanism as rotational movement of the plug member is abruptly topped. It is desirable to provide means for insuring the severe inertial forces are not transmitted to the valve actuator mechanism. This will insure that the valve actuator will provide extended service life and will facilitate less expensive manufacture of the valve actuator mechanism.
As the valve actuator and other valve components become worn, it is typical for the flow port of the plug member to become misaligned with respect to the inlet and outlet passages of the valve mechanism. When the port is misaligned with the inlet and outlet flow passages, turbulence can be developed that will impede the flow of fluid through the valve mechanism. Also, especially in large valve mechanisms, the seat surfaces and sealing surfaces of the valve body and plug member may become misaligned if the position of the plug at the end of its operational stroke becomes changed. In this case, the valve will not seal properly and must be typically disassembled for repair. Alternatively, in some cases the valve actuator may be adjusted to modify the stopping position of the plug member, depending upon the characteristics of the valve actuator. It is desirable to provide means for simply and efficiently adjusting the stopping position of the plug member within the valve body and it is also desirable to provide adjustment means that is capable of external adjustment to insure against the necessity to disassemble the valve for adjustment.
Where a high degree of seal integrity is mandatory in plug valve mechanisms, it is desirable to determine if a proper seal is established each time the plug member is shifted linearly to a sealing position. If the valve should leak even a small amount with the plug at its sealing position, then it may be necessary to disregard a meter loop measurement for the purpose of checking the accuracy of a flowmeter. It is desirable to insure that the four-way plug valve is sealing properly at each operational run of the flowmeter loop in order that the known volume of the flowmeter loop may be checked against the particular measurement of the flowmeter involved. It is desirable to provide means or insuring the seal integrity of the plug valve mechanism during each prover run.
In some cases, the tapered plug elements of lift-turn type four-way plug valves are formed to define pairs of seal grooves and sealing material, such as a suitable elastomeric or plastic material, is molded within these grooves in order to define the sealing elements of the plug. In the event these molded seal elements become worn to the point that replacement is desired, the valve must be disassembled to remove the plug element. Typically, to place the valve back in service as soon as possible, a substitute plug is installed. The plug member having the worn seal is then transferred to a repair facility where the seal grooves will be cleaned and new sealing material installed. The reconditioned plug member will then be placed in readiness for future repair operations. In other cases, the tapered plug members are formed to define grooves having small seal openings through which the sealing portion of sealing elements extend with the seal grooves being formed to mechanically retain the sealing elements against displacement from the seal groove by the forces of the flowing fluid. These types of seals are not typically satisfactory because they are rather easily extruded from the seal grooves by fluid forces and are rather easily damaged. When servicing is required, however, these types of plugs can be repaired very simply by removing the worn or damaged seals and by simply inserting replacement seals. It is desirable to provide a plug valve mechanism incorporating sealing elements that are field replaceable but which are mechanically retained within seal grooves to the extent that the seals will effectively resist ordinary seal extrusion and damage and will function quite satisfactorily at high operating pressures or under the influence of high volume fluid flow.
When tapered rotary plug valves are lifted for unseating and moved downwardly for seating movement as well as being rotated during fluid controlling movement, differential volumetric changes typically occur. The spaces defined between the valve element and the large and small extremities of the valve typically vary substantially in volume. During seating and unseating movement, the plug member is moved linearly with seals established between the plug member and the inner surfaces of the valve body. During such plug movement negative and positive fluid pressures typically develop that retard plug movement and therefore subject the valve actuator system to greater forces than might be desirable. It is desirable to provide means for insuring maintenance of a predetermined maximum pressure differential across the sealing elements of the valve during seating and unseating movement and to minimize the effect of any operator retarding forces due to positive and negative pressures.
In view of the foregoing, it is a primary feature of the present invention to provide a novel four-way lift plug type valve mechanism incorporating a dampening system that effectively reduces inertial forces that might otherwise be transmitted from the rotatable plug member to the valve actuating mechanism thereof.
It is also a feature of the present invention to provide a novel four-way lift turn type plug valve mechanism that incorporates an externally adjustable plug positioning mechanism that allows the stopping position of the plug at the end of its rotational movement to be changed without necessitating disassembly of the valve mechanism or modification of the valve actuator system.
Among the several features of the present invention is contemplated a novel lift-turn type plug valve mechanism incorporating means for checking the integrity of the seal each time the plug member is positioned at the seal position thereof.
It is also a feature of the present invention to provide a four-way lift turn type plug valve mechanism incorporating a fluid transfer system for purposes of dampening rotational movement of the plug element, which fluid dampening system incorporates a pair of schematically parallel fluid flow conduits, each including relief valves for allowing unidirectional flow of dampening fluid through each of the schematically parallel conduits.
It is a further feature of the present invention to incorporate in conjunction with a four-way lift turn type valve mechanism a plural relief valve system allowing fluid flow at different selected pressures depending upon the direction of flow through the relief valve mechanism.
It is also a feature of the present invention to incorporate in conjunction with a four-way plug valve mechanism a plural relief valve system incorporating two relief valves with the flow of fluid in one direction through the relief valve mechanism causing opening of a first relief valve while simultaneously applying a closing fluid pressure to the second relief valve and flow of dampening fluid in the opposite direction through the relief valve mechanism induces opening of the second relief valve while simultaneously assisting in closure of the first relief valve.
It is another provision of this invention to provide a novel four-way valve mechanism having the capability of compensating for volumetric changes within the valve chamber and minimizing any actuator retarding forces that might otherwise develop.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration of this entire disclosure. The form of the invention, which will now be described in detail, illustrates the general principles of the invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.